Flow measurement of particulate streams such as wet cakes, grains, cereals, dry powders, minerals, pharmaceuticals, dairy powders, chemicals, spices, snack foods, cement, resins, plastics, fibrous materials, and others may be critical to the operation and optimization of a given process. A non-contact flow meter may also be of great importance since measurements are obtained without interfering with the flow of product through the process transfer line. A non-contact flow meter is preferred for measuring the flow of some products through transfer lines since any obstruction in the line can cause buildup that may eventually result in a plugged line. In addition, by using a non-contact flow meter there is no degradation of the material since the flow is unobstructed, and the integrity of the process can be maintained. For example, a non-contact solids flow meter obtains measurements during the processing or manufacturing of food and pharmaceuticals without contamination and without compromising of the integrity of the process. There is always a concern about contamination for these type products. As examples only, some typical applications for flow/quantity measurements include, but are not limited to feed to dryers, discharge from dryers, feed to milling operations, material flow to mixers, flow from dust collectors, flow from conveyors, loading/unloading of railcars, trucks, barges and silos, and flow of grains through ducts, cement loading/unloading, flow of plastic granules, flow from cyclones, and feed to reactors.
U.S. Pat. No. 4,091,385, discloses a Doppler radar flow meter in which the flow meter comprises a radar transmitter and receiver that respectively radiates radio waves at a predetermined microwave frequency at least partially through a fluid. At least a portion of the radio waves are backscattered by the particulate matter in the path of the radiated radio waves and are picked up by the receiver. A signal processor connected to the receiver produces a signal related to the Doppler's shift in frequency between the backscattered radio waves and the radiated radio waves such that the frequency is related to the velocity of flow of the substance being measured. In particular, the flow meter is used for velocity of flow of fluids such as blood in conduits (i.e. blood vessels).
U.S. Pat. No. 5,550,537 discloses another apparatus for measuring mass flow rate of a moving medium using Doppler radar. The patent discloses a non-intrusive mass flow rate meter that includes a transceiver that transmits an electromagnetic signal of known frequency and power to illuminate a portion of moving material. The transceiver detects the magnitude and the Doppler shift of the electromagnetic signal that is reflected by material moving along the process flow as it passes through the electromagnetic field established by the signal. The transceiver then combines the magnitude of the reflected electromagnetic signal along with the Doppler shift between the frequency of the transmitted and reflected electromagnetic signals to generate an output signal related to the mass flow rate of the material. However, only a portion of the moving material is illuminated according to the U.S. Pat. No. 5,550,537. This can create errors in the mass flow rate and may provide incorrect readings as to the quantity of material that is passing through the conduit.
U.S. Pat. Nos. 5,986,553 and 6,404,344 were issued to the same inventor as the present invention and disclose an improved flow meter for measuring solid particulate flow rates by radiating the particulate flow path through a conduit such that substantially all of the particulate matter contributes to and forms backscatter energy. The backscatter energy is used to generate an electrical signal that is proportional to the consolidation of solid particulate matter flowing through the conduit. The flow meter described in U.S. Pat. No. '553 is quite sensitive to motion and is normally very accurate for most applications. However, because of its sensitivity to particulate motion, the flow meter is also sensitive to various “motions”, other than the particulate material motion, which are often present in a particulate matter distribution system. For example, the motion of a rotating screw conveyor or product dust can be sensed by the system and result in an erroneous indication of the output particulate flow rate. The 6,404,344 patent discloses a technique and method that helps avoid such errors in the calibration of the output flow rate of the particulate material.